SDR Receiver is a Software Defined Radio (SDR) that processes, demodulates and plays AM, narrowband FM and wideband FM signals.  The signals are streamed over a network from a signal server that is the source of a digitized portion of the RF spectrum.  The signal server will generally consist of a radio that is connected by USB to a host computer that is running a server application.  With a properly configured radio and the right antenna, signals that may be played through SDR Receiver typically include transmissions from aircraft (AM),  amateur transmitters/repeaters and police/fire radios (narrowband FM) and commercial broadcast stations (wideband FM).  The host computer runs a server application that accepts sampled baseband IQ signals from the radio over USB and streams the sampled signals over the network to the device running SDR Receiver.  The radio, host computer, and host server software are not provided with SDR Receiver and must be separately obtained and installed.  SDR Receiver supports RTL-SDR, Airspy HF+ and SDRplay radios.  To operate with an RTL-SDR radio, the host computer must run the rtl_tcp server application which is part of the librtlsdr open source library package and runs on Mac, PC and Raspberry Pi.  To operate with an Airspy HF+ radio, the host computer must run the hfp_tcp open source server application which runs on Mac and Raspberry Pi. To operate with an SDRplay radio, the host computer must run the rsp_tcp open source server application which runs on Mac, PC and Raspberry Pi.

The functions of SDR Receiver are divided into three tabs:

• The Stations tab has controls for frequency, mode, LNA gain, volume, and an On/Off switch that starts and stops the stream of data from the server.  The application manages lists of stations which can be entered, edited, reordered and deleted from the Stations tab.  A single list is active and the stations on the active list are displayed on the Stations tab.  A new station can be created with the + button.  Stations in the active list may be updated, moved or deleted by tapping the Edit button and using the controls that appear on the left and right of each station entry. The controls on the right enable reordering, and the controls on the left reveal Update and Delete buttons.  A swipe left on a station in the list will also reveal Update and Delete buttons.  With these buttons the frequency, description and mode of the station may be updated, and the station may be deleted. A station can also be moved by long pressing the station which will cause its image to lift, and then dragging it to a new location.

• The Lists tab provides a set of Preset lists, and the ability to create, rename and manage Custom lists.  The active list is selected from the Custom lists, and the name of the active list is highlighted in blue.  A new empty Custom list is created with the + button.  A new Custom list with the name and contents of a specific Preset list is created by selecting that list in the Preset section.  A Custom list may be renamed, deleted or moved via the Edit button or with a swipe left on the name of the Custom list. A list can also be moved by long pressing the the list which will cause its image to lift, and then dragging it to a new location.  Lists may be exported or imported in Comma Separated Values (CSV) format or in Tab Separated Values (TSV) format, to or from a file with .csv or .tsv extensions; by copy/paste to or from a text document or a spreadsheet like Apple Numbers or Google Sheets; and on iPad lists may be imported by drag/drop from a text based app or from a spreadsheet. 

• The Settings tab provides controls for:  selecting the network address of the signal server; configuring the operating parameters of the signal server and radio including the server type, sampling rate, sample size and direct sampling configuration;  settings related to signal processing functions including audio filters, squelch and tuning; and selection of CSV or TSV export data format. This tab also provides information related to help and support. 

SDR Receiver also responds to specially formatted URLs that enable the app to be controlled and launched from another application on the device.